GRACE data shows Greenland

August 2006: The Greenland Ice Sheet the second largest ice cap on Earth is now melting twice as fast than in the preceding five years, according to a US-based research team led by Chinese scientist Chen Jianli. It has been shrinking by about 240 cubic kilometres per year since 2004, researchers estimated after studying ice mass changes over Greenland between 2002 and 2005. Previous research showed that the annual loss of the Greenland ice sheet was about 90 cubic kilometres between 1997 and 2003.

The latest discovery, published in this week’s issue of Science, adds another important piece to the global warming puzzle, indicating that melting polar ice sheets are contributing to the rise of global sea levels. “Our result confirms that the island’s ice is melting at an accelerated pace,” Chen, now a geophysicist at the Centre for Space Research at the University of Texas, told China Daily on Tuesday.

Chen worked at the Shanghai Observatory for five years before pursuing a PhD in geophysics in the US. He recently received a US Presidential Early Career Award for Scientists and Engineers. In March this year, US scientists used satellite radar interferometry data to estimate that the Greenland Ice Sheet is melting by about 224 cubic kilometres annually.

However, “Some doubts remained over the result as the satellite remote sensing technique generally allows large errors,” said Chen. Chen and his research team drew their conclusions from a more accurate methodgravity field variation datacollected through the Gravity Recovery and Climate Experiment (GRACE) satellite mission. The GRACE mission was jointly launched by the National Aeronautics and Space Administration (NASA) in the United States and Germany’s Aerospace Research Centre and Space Agency (DLR) in 2002. The GRACE satellite maps the Earth’s gravity fields by measuring the distance between two identical satellites.

“We also invented a novel technique to recover and filter important signals from space background noise,” Chen said.

Chen and his team also detected that a glacier in southeast Greenland has had its highest melting rate since 2004, with annual ice loss of 90 cubic kilometres. “With GRACE, we can define each glacier’s individual ice change, which was not possible using previous techniques,” he noted. “It is a real technological advance, which provides the best ever method to study long-term climate change.” Scientists estimate that the complete melting of the Greenland cap would raise the global mean sea level by about 6.5 metres, a change which would cause the disappearance of some island countries.